95 Impact of reducing in vitro fertilization period on cleavage and blastocyst development rates

Timely availability of essential components such as pyruvate, amino acids, nucleotides, and growth factors during the early stage of development of embryos is critical for optimal blastocyst formation. The question remains whether early transfer of the presumptive zygotes into in vitro culture medium has an impact on blastocyst rate. The present study assessed whether a shorter IVF duration (12 h) compared with a longer duration (18 h) affects embryonic developmental competence by facilitating early exposure to these crucial nutrients during in vitro culture (IVC). Bovine oocytes from 54 ovum pickup sessions (753 oocytes) were subjected to IVM for 22 h in 5% CO₂ in air at 38.5°C with maximum humidity. Following IVM, oocytes underwent IVF for either 12 h (n = 367) or 18 h (n = 386) at 5% CO₂ in air at 38.5°C with maximum humidity. Post-fertilization, the oocytes underwent IVC for 7 days from IVF at 5% CO₂, 5% O₂, and 90% N₂ at 38.5°C with maximum humidity. Cleavage and blastocyst rates were calculated by dividing the number of oocytes that cleaved and developed into blastocysts by the total number of oocytes in IVC. Descriptive statistics were calculated, and Welch two-sample t-tests were conducted using RStudio (version 2024.04.1+748) to compare the different means between the two groups of IVF duration. The 12-h IVF group exhibited a cleavage rate of 71.0 ± 4.7% and a blastocyst rate of 32.3 ± 5.4%. In contrast, the 18-h IVF group showed a cleavage rate of 65.2 ± 4.1% and a blastocyst rate of 28.9 ± 4.7%. Although some improvement was observed in the 12-h blastocyst group, the differences were not statistically significant (P-values of 0.36 and 0.60 for cleavage and blastocyst rates, respectively). These results suggest that a 12-h IVF duration might offer advantages in enhancing embryonic developmental competence over an 18-h duration. This observation may be linked to the early availability of optimal metabolic and developmental components, such as pyruvate, amino acids, nucleotides, and growth factors, during the maternal-to-embryonic transition. Delayed availability of these necessary nutrients can lead to suboptimal conditions, potentially impairing energy metabolism, protein synthesis, and cellular signaling, resulting in reduced developmental competence and lower cleavage and blastocyst formation rates. We are continuing the study with larger sample sizes to confirm the preliminary findings.